Gross mineralogy and petrology using raman spectroscopy

ABSTRACT

A method may include measuring a formation sample using a Raman spectrometer to determine a formation sample characteristic, wherein the formation sample characteristic is mineral ID and distribution, carbon ID and distribution, thermal maturity, rock texture, fossil characterization, or combinations thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a nonprovisional application which claims priorityfrom U.S. provisional application No. 62/336,035, filed May 13, 2016,which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD/FIELD OF THE DISCLOSURE

The present disclosure relates generally to methods and apparatuses forevaluating gross mineralogy and petrology of a geologic formation.

BACKGROUND OF THE DISCLOSURE

The depositional processes that created certain geologic formations(hereinafter, “formations”), for example, hydrocarbon-bearingformations, and diagenetic processes that reformed portions of thehydrocarbon-bearing formations were heterogeneous. Knowledge of thegross mineralogy and petrology of a formation and/or sections of aformation may provide insight into areas of interest in the formation.For instance, gross mineralogy and petrology may identify spots forfracking, for instance, in a shale formation.

Traditional methods of determination of gross mineralogy and petrographyare performed on formation samples with different sets of equipment andrequire some degree of qualitative analysis by a geologist. Thesetraditional methods often are subjective and may result inmisidentification of gross mineralogy and petrography characteristics.For instance, X-Ray Diffraction (XRD) may provide gross mineralogy of ahomogenized sample, but such characteristics as grain size, pore size,and crystalline structure are lost in the sample preparation. XRD alsodoes not provide a measure of organics of the formation sample. SEM/EDS(Scanning Electron Microscope/Energy Dispersive X-ray Spectroscopy) mayidentify grain size and structure of a formation sample, but does notprovide a direct molecular analysis. In addition, EDS is limited toelemental analysis and neither EDS nor SEM provides a measure oforganics of the formation sample. X-Ray Fluorescence (XRF) is limited toelemental analysis, which may require correlation to equate theelemental analysis to mineralogy of a sample. XRF does not provide ameasure of organics of the formation sample. Laser-induced breakdownspectroscopy (LIBS), like XRF, is limited to elemental analysis and doesnot provide a measure of organics in the formation sample. LIBSvaporizes a portion of the formation sample, which may affectreproducibility of the results. Pyrolysis may determine thermal maturityof a formation sample, but the formation sample is physically andchemically altered in this destructive test, adversely impactingreproducibility of results. Further, pyrolysis results may be skewed bythe presence of bitumen in a formation sample.

SUMMARY

The present disclosure provides for a method. The method includesmeasuring a formation sample using a Raman spectrometer to determine aformation sample characteristic, wherein the formation samplecharacteristic is mineral ID and distribution, carbon ID anddistribution, thermal maturity, rock texture, fossil characterization,or combinations thereof.

The present disclosure further provides for a method. The methodincludes imaging a sample surface, generating a digital atlas substrate,mapping an area of interest, and layering information on a digital atlassubstrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale. In fact, the dimensions of the variousfeatures may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a flowchart depicting the formation of a digital atlasconsistent with at least one embodiment of the present disclosure.

FIGS. 2A, 2B are graphical depictions of digital sampling methodologyconsistent with embodiments of the present disclosure.

FIG. 3 is a combined optical and false color hyperspectral image asdescribed in Example 2.

FIG. 4 is a combined optical and false color hyperspectral image asdescribed in Example 2.

FIG. 5 is an axis orientation in polar plot as described in Example 2.

FIG. 6 is an ex-situ measurement system consistent with certainembodiments of the present disclosure.

FIG. 7 is an in-situ measurement system consistent with certainembodiments of the present disclosure.

FIG. 8 is an in-situ measurement system consistent with certainembodiments of the present disclosure.

FIG. 9 is an in-situ measurement system consistent with certainembodiments of the present disclosure.

DETAILED DESCRIPTION

A detailed description will now be provided. The following disclosureincludes specific embodiments, versions and examples, but the disclosureis not limited to these embodiments, versions or examples, which areincluded to enable a person having ordinary skill in the art to make anduse the disclosure when the information in this application is combinedwith available information and technology.

Various terms as used herein are shown below. To the extent a term usedin a claim is not defined below, it should be given the broadestdefinition persons in the pertinent art have given that term asreflected in printed publications and issued patents. Further, unlessotherwise specified, all compounds described herein may be substitutedor unsubstituted and the listing of compounds includes derivativesthereof.

Further, various ranges and/or numerical limitations may be expresslystated below. It should be recognized that unless stated otherwise, itis intended that endpoints are to be interchangeable. Where numericalranges or limitations are expressly stated, such express ranges orlimitations should be understood to include iterative ranges orlimitations of like magnitude falling within the expressly stated rangesor limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.;greater than 0.10 includes 0.11, 0.12, 0.13, etc.).

“Formation” as used herein is a body of strata of predominantly one typeor combination of types. A formation may include one or more“intervals,” which are subdivisions of a formation. A“hydrocarbon-bearing formation” is a formation in which one or moreintervals include at least one hydrocarbon.

In certain embodiments of the present disclosure, a formation samplemeasurement instrument, such as a Raman spectrometer, or a Ramanspectrometer in conjunction with other technologies including, but notlimited to XRD, SEM/EDS, infrared (IR) microscopy, XRF, LIB S, anddigital optical microscopy (hereinafter referred to as “non-Ramantechnology”) may be used to measure formation sample characteristics. Insome embodiments, a particular formation sample characteristic may bemeasured with a Raman spectrometer. In other embodiments, a particularformation sample characteristic may be measured with a non-Ramantechnology. In certain embodiments, a formation sample characteristicmay be measured with a Raman spectrometer and the same characteristicmay be measured with a non-Raman spectrometer. In other embodiments, aformation sample characteristic may be measured with a non-Ramantechnology and the same characteristic may be measured with a Ramanspectrometer or a different non-Raman technology. In some embodiments,the Raman spectrometer uses confocal Raman spectroscopy to measure thecharacteristics of the formation sample.

Examples of characteristics of a formation sample may include, but arenot limited to, optical image, mineral identification (“ID”) anddistribution, carbon and/or organic matter ID and distribution, thermalmaturity, rock texture, lithology and fossil characterization. Anoptical image is an image of the formation sample or a portion of theformation sample formed by the refraction or reflection of light.Mineral ID and distribution is the identification of minerals in theformation sample and their location within the formation sample. MineralID and distribution includes, but is not limited to clay identificationand distribution. Carbon and/or organic matter ID and distribution isthe differentiation of different carbon types and or organic phaseswithin the formation sample, such as kerogen and bitumen, and thedistribution of those carbon types and organic phases within theformation sample. Thermal maturity is the extent of heat-drivenreactions that alter the composition of organic matter, including, butnot limited to, the conversion of sedimentary organic matter topetroleum or cracking of oil to gas. Rock texture of a formation sampleincludes grain size distribution, pore size distribution, mineral phasedistribution, grain orientation, grain shape and angularity, porositydistribution, and bedding planes. Fossil characterization includes theidentification, distribution and measurement of fossil markers andassociated organic and inorganic material with Raman or other non-Ramantechnology.

Measurement of formation samples may be performed ex-situ or in-situ. Inex-situ measurement, a formation sample is removed from the formation.For example and without limitation, removal of a formation sample may bethrough retrieval of a core sample from the formation, by capture ofdrill cuttings, such as from a shale shaker, chemical extraction orobtaining a homogenized powder . . . . In certain embodiments, theformation sample may be transported to a measurement facility (either onthe wellsite or elsewhere), such as a laboratory, or removed fromprocess equipment such as a shale shaker. Measurements are performedthrough the use of the formation sample measurement instrument, such asa Raman spectrometer or by non-Raman technology. An example ofmeasurement system for measurement of formation samples ex-situ isdepicted in FIG. 6. FIG. 6 depicts ex-situ measurement system 500. Inex-situ measurement system 500, drill string 530 is positioned withinwellbore 510. As drilling is performed by drill string 530, wellborefluid containing cuttings, drilling mud, and formation fluids, forexample, are withdrawn from wellbore 510 to surface 520. The wellborefluid is separated by cuttings separator 540. Cuttings separator 540 maybe, for example and without limitation, a shale shaker. Drilling mud isremoved from cuttings separator 540 through drilling mud discharge 550and cuttings are removed from cuttings separator 540 through cuttingsdischarge 560. Cuttings may be cleaned and otherwise processed incleaning system 570 to ready the cuttings for analysis. The cleanedcuttings may then be analyzed using analyzer 590. Analyzer 590 may be aRaman spectrometer or a non-Raman spectrometer. In some embodiments,cuttings may be transported using sample conveyance 580 through cleaningsystem 570 and to analyzer 590 using sample conveyance 580. Sampleconveyance 580 may be a conveyor, carousel, or other moving system. Inother embodiments, analyzer 590 may be positioned in a probe thattranslates over sample cuttings.

In in-situ measurement, the formation sample measurement instrument asdescribed hereinbelow is positioned in the formation, such as into awellbore, and measurements performed on the formation itself, forinstance, the wall of the wellbore. While measurement of formationsample characteristics are described below with respect to ex-situmeasurement, one of ordinary skill in the art with the benefit of thisdisclosure will understand that the measurements may be made in-situ aswell.

The formation sample measurements may be collected in a digital atlas.In a digital atlas, formation characteristics of portions of theformation sample may be associated or “layered,” allowing a user toanalyze, query, overlay, create animations, perform a digital zoom, orscroll and pan over the digital representation of the formation sample.

High-Resolution Digital Optical Microscopy

In certain embodiments, as shown in FIG. 1, digital atlas formation 100may begin by imaging the formation sample surface (image sample surface110) using, for example, automated high-resolution digital opticalmicroscopy. In image sample surface 110, formation samples may be fixedto a mounting substrate and placed on an encoded XYZ-microscope stagefor optical imaging using, for instance, wide-field illuminationtechniques. Wide-field illumination techniques include, but are notlimited to, conventional reflective or transmissive illumination,polarized light, fluorescence, and dark-field. Images of formationsample surfaces may be captured on a digital camera through a microscopeobjective and digitally stored in a non-transitory media. In certainembodiments, the formation sample may be moved through the field of viewof the microscope objective, or the field of view may be moved over thesample using a digital sample methodology. In certain embodiments, suchas in-situ measurement, the formation sample measurement instrument maybe moved over the formation. In yet other embodiments, laser scanningmay be performed where a focused laser spot is optically translatedacross a fixed sample surface.

With direction to FIG. 2A, digital sample methodology 200 may includeoverlapping images of the formation sample surface. As shown in FIG. 2B,digital sample methodology 200′ may include representative, selected, orrandomly determined images of the sample surface. Representative imagesmay be images determined optically by a user or via algorithm to berepresentative of the formation sample surface. Selected images may beimages of a formation sample surface determined optically to be ofinterest, such as, for example, examination by a user using the nakedeye. “Of interest” portions of sample surface may be micro-fractures,fossils, coloration changes, organic features, inorganic features,specific formation beds or other portions of the sample. Random imagesmay be selected by random computer algorithm, for example. The imagescaptured by the encoded microscope stage may be used to generate adigital atlas substrate of formation sample surfaces (element 120 ofFIG. 1). In addition to capturing images to form the digital atlassubstrate, images captured by the encoded microscope stage may be usedto develop 3-D topography of the formation sample surface. The 3-Dtopography may be developed by identifying regions in the image whichare in focus. Additionally, images captured by the encoded microscopestage may be used to identify areas of interest for further study byhyperspectral mapping microscopy as described herein below, and analyzerock texture as described herein below. Information regarding 3-Dtopography of the formation sample surface and rock texture may be“layered” onto the digital atlas substrate to form the digital atlas inlayer information on digital atlas substrate 140 in FIG. 1. “Layering,”as described herein, means associating information regarding theformation sample surface with the particular image or portion of aparticular image to which it pertains. In certain embodiments,information regarding the formation sample surface may be associatedwith, i.e., layered onto, individual pixels or groups of pixels of theimages. Optical microscopy may be performed at optical resolution.Optical resolution may refer to a scale of greater than 500 nm.

In certain embodiments, in addition to, or in lieu of, opticalmicroscopy, the digital atlas substrate may be formed through use ofimages obtained from SEM. In other embodiments, images obtained from SEMmay be used as a layer in the digital atlas substrate.

Hyperspectral Mapping Microscopy

In certain embodiments, areas of interest may be identified from thehigh-resolution digital microscopy and may be examined usinghyperspectral mapping microscopy (130). In certain embodiments, imagesample surface (110) may be omitted and hyperspectral mapping microscopymay be performed on portions of the sample surface otherwise identifiedas of interest, such as, for example, by visual identification.Hyperspectral mapping microscopy may be performed, for instance, usingsample-scanning spectroscopy or XRF. Examples of sample-scanningspectroscopy include LIBS, IR, fluorescence, time-resolved spectroscopy,and confocal laser microscopy, such as, for example and withoutlimitation, Raman spectroscopy. Sample-scanning confocal lasermicroscopy may be performed by focusing an excitation laser through themicroscope objective to form a diffraction-limited focused laser spotonto sample surfaces in areas of interest identified through automatedhigh-resolution digital microscopy. By focusing the diffraction-limitedfocused laser spot on the formation sample, light is emitted from theformation sample. Light emitted from the formation sample in thediffraction-limited focused laser spot may be collected and passedthrough a spectrograph, such as a Raman spectrograph, for separation bywavelength and analysis of the emitted light spectrum through use of,for instance, a digital camera. The encoded XYZ-microscope stage may beused to raster the sample surface through the laser focus and recordemitted light spectra from focused spots to generate a hyperspectralmulti-point scan, line scan or map of the emitted light in the area ofinterest.

Individual light spectra may be compared to a library of, for example,Raman spectra of minerals, clays, and organic phases to identify rockconstituents, the abundance of rock constituents and distribution ofrock constituents. One example of a digital library is the RRUFFproject. Examples of rock constituents may include, for example, mineraltypes, quartz, clay-types (including, but not limited to swelling claysand non-swelling clays), kerogen types, and bitumen. By identifying therock constituents, the abundance of rock constituents and thedistribution of rock constituents, formation characteristics such asquartz-to-clay ratio (a measure of rock brittleness), clay type, andtotal organic content (TOC) may be calculated. In certain embodiments,spectral analysis, such as of organic phases, may include peak-fitting,factor analysis and other chemometrics techniques to correlate thecomplex Raman spectra of organic deposits with carbon types (e.g.kerogen and bitumen) and thermal maturity indices.

For purposes of this disclosure, chemometrics is the application of dataanalysis techniques to analyze usually large amounts of chemical data.In certain embodiments, chemometrics analysis may be used to identifyrelationships between observable and underlying (latent) variables andto predict behaviors or properties of systems, for example in acalibration. Applied to spectroscopic chemical data, including, but notlimited to Raman spectra, chemometrics analyses may be based on theprincipal of superposition, i.e., a spectrum is composed of the sum ofits parts. For example and without limitation, the Raman spectrum from amixture of non-interacting chemicals can be reconstituted by summing theindividual Raman spectra from each of the components in the mixture.Examples of chemometrics techniques for spectral data include PrincipalComponents Analysis, which seeks to reduce the data to a minimum numberof components, Factor Analysis, which seeks to understand relationshipsbetween variables in data, Classical Least Squares analysis, which isbased on linear combinations of measured pure components and PartialLeast Squares analysis, an inverse least squares technique that seeks tocorrelate the variance in the independent and dependent variables of thedata set, working in absence of measured pure components.

Information obtained from hyperspectral mapping microscopy, includingbut not limited to rock constituents, the abundance of rock constituentsand distribution of rock constituents, quartz-to-clay ratios, clay type,and total organic content (TOC) may be layered on to the digital atlassubstrate (140).

In other embodiments, a laser wavelength is selected to excite thefluorescence of rock constituents and a hyperspectral fluorescence mapis recorded to identify and analyze the intensity and distribution offluorescent constituents, such as Tasmanites fossils. In anotheralternative, the excitation is tuned to the infrared and an absorbancespectrum map is collected. In yet another alternative, pulsed laser isfocused on the sample and a time-gated detector is implemented tocollect time-resolved spectral maps (e.g. fluorescence lifetime) orelemental maps are performed through laser-induced breakdownspectroscopy (LIBS). This information may be layered onto the digitalatlas substrate (140).

Rock Texture Image Analysis:

In certain embodiments, rock texture image analysis (element 150 inFIG. 1) may be performed on the digital atlas for a formation sample.Optical imaging and hyperspectral mapping may generate a large amount ofrock formation image data that contains information about the makeup andtexture of the rock of the formation sample, i.e., the rock fabric.Advanced image analysis techniques may be used on the rock formationimage data to characterize, for instance, the size of grains and porespaces of the formation sample or portion of the formation sample.

The compilation of images and data in the digital atlas may be processedusing one or more image processing techniques. Some information, such asa digital atlas layer corresponding to the distribution of pyrite asidentified with for example, hyperspectral Raman mapping or SEM/EDSelemental analysis, may be analyzed for mineral grain size, grain shape,and distribution. Example image processing techniques include, but arenot limited to, color-based segmentation, shape identification, HoughTransforms, color inversion, boundary tracing, Red/Green/Blue (RGB)color map filtering, distribution statistics, noise removal and imagemorphology or morphological operations such as dilation and contraction.To perform these techniques, images may be enhanced to increasecontrast, or color saturation. Some steps may be performed manually.Shapes such as circles, rectangles, squares, and triangles may be fit toparticular features, either visual features, or specific featuresidentified by spectral analysis, such as pyrite or quartz.

By applying digital image processing, the need for a highly trainedperson may be removed, and the analysis performed objectively. Thealgorithms and processing can be done on the entire image, or onspecific areas of interest identified through steps such as highresolution imaging, or hyperspectral mapping.

In certain embodiments, determination of formation characteristics maybe performed in-situ. For instance, during drilling, a Ramanspectrometer, or a Raman spectrometer in conjunction with non-Ramantechnology, hereinafter referred to as the “in-situ measurement tool”may be included as part of an MWD/LWD string, tubular deployed method,or fiber optic string. The in-situ measurement tool may rotate with thedrill string, moving the field of view, for instance, in a helical path,and the sidewall of a borehole may be examined. In other embodiments,the in-situ measurement tool may measure the formation characteristicsby measuring drill cuttings that flow past the in-situ measurement tool.In embodiments where the sidewall or cuttings are measured, results maybe bulk averaged for mineral analysis, identification of organics,lithologies and formations, and total organic carbon. An example of anin-situ measurement system is depicted in FIG. 7. In-situ measurementsystem 600 may include in-situ measurement tool 620 which includesanalyzer 590. Analyzer 590 may be a Raman spectrometer, or a Ramanspectrometer in conjunction with non-Raman technology. In-situmeasurement tool 620 is positioned within wellbore 510. As further shownin FIG. 7, in-situ-measurement tool 620 may use helical path 630 toreach formation of interest 610. Analyzer spot 640 may be projectedagainst wellbore wall 514 and/or drill cuttings 516 (shown as analyzerspot 640, which may be a laser spot) along helical path 630, therebymoving the field of view of analyzer 590.

In other embodiments, after completion of drilling, an in-situmeasurement tool may be lowered into the formation via wireline. Byrotating the in-situ measurement tool, for instance, in a helical path,the sidewall of a borehole may be examined. The in-situ measurement toolcould use a laser scanning and optical technique to translate the laseracross the sidewall surface. In another embodiment, the in-situmeasurement tool could be conveyed into the formation via coiled tubingor similar tubular type deployment. An example of such an in-situmeasurement system is shown in FIG. 8. FIG. 8 depicts uses of in-situmeasurement system 600 after completion of drilling. In-situ measurementtool 620 may be lowered along helical path 630. Analyzer spot 640 may beprojected against wellbore wall 514 along helical path 630, therebymoving the field of view of analyzer 590. In-situ measurement tool 620may be lowered into wellbore 510 using wirelines or tubing conveyance660, which connects with wireline or tubing 650 to in-situ measurementtool 620. Additionally, an in-situ measurement tool could use a caliperor other similar device to move the tool against the side of thewellbore and interrogate a specific area. Additionally, in yet anotheroption, the in-situ measurement tool could be a fiber optic conveyedsystem where, for example, a probe is located at the end of the fiberoptic and part or all of the remaining components of the Ramanspectrometer or non-Raman technology is at the surface. An example ofsuch an embodiment is depicted in FIG. 9. FIG. 9 includes in-situmeasurement system 600. Probe 680 is conveyed via fiber optic cable 690into wellbore 510 to formation of interest 610 along helical path 630.Spectrometer 670 and associated electronics may be located on surface520.

EXAMPLES

The disclosure having been generally described, the following examplesshow particular embodiments of the disclosure. It is understood that theexample is given by way of illustration and is not intended to limit thespecification or the claims.

Example 1

Hyperspectral Raman maps may reveal the location of chemical domains.Image segmentation analysis of domains may characterize the count,distribution, size, shape, and structure of domains. In a thin section,mounting material, e.g. epoxy, may infiltrate large pores and fractures.Mounting material may have a characteristic Raman or fluorescencesignature, or a unique color, and so may be identified and characterizedas to size, shape, and distribution in hyperspectral maps or digitalatlas images. In Example 1, mounting material domains are to beidentified by applying a filter to the image to show the RGB pixels thatmatch the color of the mounting material. A statistical distribution ofthese pixel locations, and size of colored regions may be used toindicate the porosity and pore sizes.

Example 2

The method outlined in Example 1, may be used, for example, for a singlepyrite group. In Example 2, optical image and hyperspectral coloredimages will be used to form the digital atlas. Single images, oroverlaid images are to be used to identify pyrite. Using imageprocessing software, or programming (such as MATLAB) to segment theimage, shapes are to be fit to features and statistics reported.Combined optical and false color hyperspectral image 300 is shown inFIG. 3. Using a RGB filter or threshold, combined optical and falsecolor hyperspectral image 300 will be converted to a 2 channel image,thereby leaving only yellow pyrite. Using MATLAB software or by hand, arectangle will be fitted to a pyrite grain as depicted in FIG. 4. FIG. 4depicts combined optical and false color hyperspectral image 400 withfitted rectangle 410. The length and width of the rectangle may then bemeasured, as well as the centroid pixel location determined. The degreeto which the rectangle shape fits the grain will be determined. Theorientation of long axis (degrees off of 0° in standard coordinatesystem) will then be identified. The distribution of axis orientation ina polar plot may be reported as shown in FIG. 5. The statisticaldistribution of all pyrite across the image will be found and thestatistical distribution reported. The analysis described herein withrespect to pyrite will then be repeated for quartz, carbon, and fossils.

Depending on the context, all references herein to the “disclosure” mayin some cases refer to certain specific embodiments only. In other casesit may refer to subject matter recited in one or more, but notnecessarily all, of the claims. While the foregoing is directed toembodiments, versions and examples of the present disclosure, which areincluded to enable a person of ordinary skill in the art to make and usethe disclosures when the information in this patent is combined withavailable information and technology, the disclosures are not limited toonly these particular embodiments, versions and examples. Other andfurther embodiments, versions and examples of the disclosure may bedevised without departing from the basic scope thereof and the scopethereof is determined by the claims that follow.

1. A method comprising: measuring a formation sample using a Ramanspectrometer to determine a formation sample characteristic, wherein theformation sample characteristic is selected from the group consisting ofmineral ID and distribution, carbon ID and distribution, thermalmaturity, lithology, rock texture, fossil characterization, andcombinations thereof.
 2. The method of claim 1 further comprising makingan optical image of the formation sample.
 3. The method of claim 1further comprising measuring a formation sample to determine theformation sample characteristic using XRD, SEM/EDS, infrared (IR)microscopy, XRF, LIBS, or combinations thereof.
 4. The method of claim1, wherein the measurement is performed in-situ or ex-situ.
 5. Themethod of claim 4, wherein the measurement is performed ex-situ and theformation sample is a drill cutting, a core sample, chemical extract orhomogenized powder.
 6. The method of claim 4, wherein the measurement isperformed in-situ using an in-situ measurement tool, wherein the in-situmeasurement tool is part of an MWD string, a LWD string, tubulardeployed method, fiber optic string or suspended from a wireline. 7-21.(canceled)